A study of optimum material for SAW bonded wafer

We have proposed the use of a lithium tantalate (LiTaO₃)/sapphire bonded substrate for compensation of temperature coefficient of frequency (TCF) in surface acoustic wave (SAW) duplexers. However, in the specific use case of a Band 8 SAW duplexer on Universal Mobile Telecommunications System (UMTS), this bonded substrate has exhibited spurious response in the pass-band. In this paper, we analyzed the spurious response by Finite Element Method (FEM) simulation and found that the spurious could be suppressed effectively by optimizing the cut angle of the LiTaO₃ substrate. Moreover, we fabricated a Band 8 SAW duplexer with the optimized cut angle and obtained experimentally good insertion loss without degradation by the spurious response. The measured insertion losses of the duplexer were 2 dB and 2.5 dB at Tx and Rx bands, respectively.